To provide a small optical pickup capable of realizing interchangeability among numerous kinds of optical disks with a simple structure and stably detecting signals even in the case where a polarizing detection optical system is used.

A laser beam emitted from an SHG blue laser unit 1 and a red semiconductor laser unit 2, each of which has a photodetector, is made a parallel light through collimator lenses 3, 4, and then combined through a dielectric multi-layer film mirror 5 so as to propagate on the same optical axis. This dielectric multi-layer film mirror 5 is constituted such that it transmits light with a wavelength of less than 500 nm in both P and S waves and that it reflects light with a wavelength of 500 nm or above. The light penetrating through or reflected by this mirror 5 is transmitted through a polarizing hologram 6 and a wavelength plate 7 and converged on an optical disk 10 with an objective lens 9.